Kikuchi Kensuke, Matsushita Norihisa, Suzuki Kazuo, Hogetsu Taizo
Laboratory of Forest Botany, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan.
Laboratory of Forest Microbiology, College of Bioresource Sciences, Nihon University, 1866 Kameino, Fujisawa-shi, Kanagawa, 252-8510, Japan.
Mycorrhiza. 2007 Oct;17(7):563-570. doi: 10.1007/s00572-007-0131-8. Epub 2007 May 22.
Under laboratory conditions, spores of ectomycorrhizal fungi usually germinate very poorly or not at all. In a previous study, we showed that spores of the ectomycorrhizal fungus Suillus bovinus germinated through the combination of activated charcoal treatment of media and co-culture with seedlings of Pinus densiflora, which suggested that some substances contained in root exudates induced the germination. Among the compounds reported from root exudates, flavonoids have been elucidated to play various and substantial roles in plant-microbe interactions; we therefore investigated the effects of flavonoids on basidiospore germination of S. bovinus by the diffusion gradient assay on water agar plates pretreated with charcoal powder. Seven out of the 11 flavonoids tested, hesperidin, morin, rutin, quercitrin, naringenin, genistein, and chrysin, had greater effects than controls, whereas flavone, biochanin A, luteolin, and quercetin showed no positive effects. The effective concentration presumably corresponded to several micromolar levels, which was equivalent to those effective for pollen development, nod gene induction, and spore germination of F. solani f. sp. pisi and AM fungi. The results suggest that flavonoids play a role as signaling molecules in symbiotic relationships between woody plants and ectomycorrhizal fungi.
在实验室条件下，外生菌根真菌的孢子通常萌发很差或根本不萌发。在先前的一项研究中，我们发现外生菌根真菌牛肝菌（Suillus bovinus）的孢子通过培养基的活性炭处理以及与赤松幼苗共培养而萌发，这表明根系分泌物中含有的某些物质诱导了萌发。在已报道的根系分泌物化合物中，黄酮类化合物在植物-微生物相互作用中发挥了多种重要作用；因此，我们通过在经炭粉预处理的水琼脂平板上进行扩散梯度试验，研究了黄酮类化合物对牛肝菌担孢子萌发的影响。所测试的11种黄酮类化合物中有7种，即橙皮苷、桑色素、芦丁、槲皮苷、柚皮素、染料木黄酮和白杨素，其效果比对照更好，而黄酮、鹰嘴豆芽素A、木犀草素和槲皮素则没有积极作用。有效浓度大概相当于几微摩尔水平，这与对豌豆根腐病菌（Fusarium solani f. sp. pisi）和丛枝菌根真菌的花粉发育、结瘤基因诱导及孢子萌发有效的浓度相当。结果表明，黄酮类化合物在木本植物与外生菌根真菌的共生关系中作为信号分子发挥作用。
